In manufacturing orders OE is able to assemble 1+ components into 1 product and when the mrp_subproduct is installed, OE extends to support: 1 Component -> 1 Product + (1+ Subproduct). This is good but what if the yield of product is always variable? For example, 1000kg fresh carrots(components) -> [500~600kg carrot dices(product, yield is variable] + 500~400 kg carrot slices[subproduct, yield is variable], just forget the wastage.

The fact is in the vegetables processing industry above-alike, let me say, Food Manufacturing Industry, the product yield is always variable which largely depends on the materials(components) quality as you can easily imagine.

Just added start

To: Ad Libitom - When there is no fixed ratio between product & component, for example, the materials to be process is 10kg, but the yield of both product & subproduct are variable(depending the quality, the yield is not known until production is finished), in this case how can I pre-define the qty for product in the BOM?

To:Pierre Cogitae - Without a pre-defined BOM, it seems impossible to create a MO. Correct me if I am wrong.

This is an operational context where the use of standard cost and yield is applicable. At the end of each transformation of raw materials, factory has to declare the actual produced quantity, as well as the sub-product (if any) and the wastage. The Bom process seems to solve the issue.
look at http://www.netcerto.eu/en/openerp-possibilities/manufacturing-module

Thanks both. I believe I hv just been going through carefully the doc of mnfg module for the 2nd time but am still not clear what is the way out. Please see the INSERTED TEXTS to my question and hope for a pointer soon.

Any ideas on this out there yet? I have a similar issue where I have to put frames of honeycomb into inventory. Product is sold by the lb (weigh each frame when sold), but the weight of each frame varies. When sold, the product is wrapped and boxed, so there is a fixed mfg component to add to the variable raw material.